1. Field of Invention
The embodiment of the present invention relates generally to a converter and method for controlling the same, and more particular, to a direct current to direct current (DC-DC) converter and method for controlling the same.
2. Description of Related Art
With the developments of science and technology, the range of the output voltage of power-supplying electronic products is becoming wider. For example, electric automobile charging stations are used to provide electric power to various types of electric automobile in which batteries of these various types of electric automobiles may require different rated voltages. Therefore, the electric automobile charging stations have to provide a wide range of output voltages so as to meet the requirements of the various types of electric automobiles.
The full bridge zero-voltage switch (ZVS) converter, such as, phase-shifted full bridge converter and complementary full bridge converter, has the characteristics of wide output-voltage range which satisfies the industry's requirement for the power-supplying electronic products. For a full bridge zero-voltage switch converter under the same output current, the efficiencies of the converter under high-voltage output and low-voltage output are compared. The results indicates that when the effective duty ratio is greater, the output voltage of the full bridge zero-voltage switch converter is higher, thereby the converter can accomplish the zero-voltage turn-on, and the efficiency of the converter is also higher. Whereas when the output voltage of the full bridge zero-voltage switch converter is lower, the effective duty ratio thereof is smaller. Under this circumstance, since the switch frequency remains constant, the switch loss is almost the same as that under the high-voltage output.
However, because of the resonant inductor flow current, the loop-current is present inside the full bridge zero-voltage switch converter for a long time, and hence the conduction losses under low-voltage output and the high-voltage output are almost the same. Therefore, when the output current is constant, the power under low-voltage output is smaller, which leads to a relatively greater loss. As a result, under low-voltage output, the efficiency of the full bridge zero-voltage switch converter is greatly decreased.
Many efforts have been devoted trying to find a solution of the aforementioned problems. Nonetheless, there still a need to improve the existing apparatus and techniques in the art.